Grade 9 Chemistry, please help!

The tilt of the earth's axis of rotation is responsible for the a) ocean's tides. b) size of the moon. c) brightness of stars. d) earth’s seasons.

Sally is making a model of a magnesium atom with an atomic mass number of 24 for her chemistry class. she has foam balls for the protons, neutrons, and electrons. she has added 6 neutrons to her model so far. how many more neutrons does she need to add to complete her neutral atom of magnesium?

Ineed ! i have no clue how to do this problem.